With the explosion of the telecommunications market there is a strong pressure towards miniaturization and cost-effective realization of transceivers for digital telecommunications. This also affects the analog front-ends of these transceivers. As a result, there is a strong trend towards a high degree of integration of these front-ends, together with a reduction of the power consumption in combination with a high performance. In addition, the front-ends should be flexible, in order to cope with multiple standards, different bandwidths, different modulation schemes, . . . The classical superheterodyne front-end architectures do not immediately meet these requirements. For example, at the receiver side of a superheterodyne front-end the down-conversion from RF frequencies down to baseband as well as the channel filtering are performed in the analog domain. For a high flexibility it would be useful to perform the down-conversion and channel filtering at least partially in the digital domain. Further, the degree of integration of a superheterodyne front-end is low, since several high-frequency bandpass filters are required. These filters cannot be integrated easily with silicon IC technologies. Even if it would be possible to realize these filters either on chip with non-standard technology steps such as micromachining, or on an insulating MCM substrate, an architectural study is required since such filter realizations will most likely have a different performance than the commercially available bandpass filters (e.g. SAW filters). Hence, it is clear that for the design of miniaturized transceivers at a low cost, with low power and a high performance, serious efforts will be required for the architectural design of the front-ends, yielding extensions or alternatives to superheterodyne architectures. Traditionally, architectural design of mixed-signal front-ends is performed manually, using experience and simplified calculations. This approach, however, yields specifications for the analog circuits that are often too conservative. Further, such study often excludes the exploration of new architectures. In the last few years attempts have been made to use simulations during the architectural design. In this way, one could make architectural explorations without actually having to design each alternative.
Several solutions have been proposed for high-level simulation of mixed-signal architectures. Such simulations are often based on an extension of a high-level simulation approach of digital systems. Current state of the art software for system level simulations can be found in both free (Ptolemy) and commercial tools (MATLAB, HP-ADS, SPW). [Ptolemy of Berkley], [HP-ADS of Hewlett-Packard], [SPW of Cadence], [MATLAB/SIMULINK].
All available tools use a baseband and/or an equivalent low-pass signal to represent signals. Major drawbacks of these tools are the following:                A signal consists out of one baseband signal or one equivalent low-pass signal. This makes it difficult to process a modulated carrier together with its harmonics.        The numerical performance is sub-optimal in most cases. This can be a main drawback when analyzing e.g. the bit-error-rate (BER) of a system using a Monte-Carlo simulation. Only MATLAB (using block processing) gets the most numerical computations out of the computer. Feedback loops in the systems can be handled by all packages. Though, this can reduce the simulation speed significantly (e.g. MATLAB is inefficient on a sample-by-sample bases)        The parameters specified for the different analog circuits must be transformed into simulation parameter. E.g. an analog continuous-time filter must be converted into a discrete-time equivalent model in order to perform the simulations. This discrete-time equivalent is only required for simulation purposes and is furthermore of no particular interest for the designer.        Defining the parameters of the simulation environment is left to user. E.g. the sampling frequency and the carrier frequency of the bandpass simulation need to be specified by the user. This is in contrast with the fact that user is interested with certain frequency band, irrespective of the carrier frequency/sampling frequency used during the simulation.        Hewlett-Packard provides high-level mixed-signal simulation application HP-ADS by combining a high-level simulator, which was originally intended for digital systems (Ptolemy), with a dedicated analog simulator (the envelope simulator). Its main limitation comes from the fact that both the HPtolemy and the envelope simulator are not really complementary to each other. HPtolemy is a data flow simulator that can simulate with either baseband signals or equivalent low-pass signal representations. The sampling rate might change in the network, but the signals are limited to only 1 baseband signal or 1 equivalent low-pass signal. This makes it impossible to represent a signal together with its harmonics. The envelope simulator—on the contrary—is capable of representing multi-carrier signals. However, it has the main disadvantage that all carrier frequencies are common to all circuits and all circuit nodes in the envelope simulator. In addition, all circuits are simulated with one and the same sampling frequency. Hence, the envelope simulator looses a lot of performance when the sampling rates and/or the carrier frequencies change in the system.        